Lunar Reconnaissance Orbiter (LRO) Thermal Design Drivers and Current Thermal Design Concept

A. J. Mastropietro*, Cynthia Simmons@, William Chang@, Christine Cottingham#, Charles Baker* *NASA Goddard, @Edge Space Systems, Inc., #Lockheed Martin, Inc. August 8, 2005

1 Outline

• LRO Mission Objectives • Historical Perspective • Mission Overview • Mission Timeline • Rapidly Evolving Spacecraft Concept • Lunar Thermal Environment • LRO Thermal Design Challenges • Lessons Learned from Early Modeling • Beyond LRO? • Conclusions

2 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) 2008 Lunar Reconnaissance Orbiter (LRO) Mission Objectives First Step in the Robotic Lunar Exploration Program

LRO Objectives

• Characterization of the lunar radiation environment, biological impacts, and potential mitigation. Key aspects of this objective include determining the global radiation environment, investigating the capabilities of potential shielding materials, and validating deep space radiation prototype hardware and software.

• Develop a high resolution global, three dimensional geodetic grid of the Moon and provide the topography necessary for selecting future landing sites.

• Assess in detail the resources and environments of the Moon’s polar regions.

• High spatial resolution assessment of the Moon’s surface addressing elemental composition, mineralogy, and Regolith characteristics

3 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) Historical Perspective Lunar Exploration Past and Present Clementine robotics preparing the way 1994 Ranger 1961-1965 Luna 1959-1976 MUSES-A 1990

Surveyor 1966-1968

Zond 1965-1970 Lunar Prospector 1998

ESA SMART-1 Lunar Orbiter (2005-...) 1966-1967

Selene (2007)

LRO 2008

Lunokhod 1970 Apollo 1969-1972 4 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) Historical Perspective (con’t)

• Existing Data Sets – Earth Based Telescopes – Ranger – Surveyor – Lunar Orbiter – Apollo Photography & Laser Altimetry – Earth Based Radar – Clementine Imaging, Gravity, & Topography – Lunar Prospector Elemental Maps – Soviet Data

• What is missing? Mars MOLA Geodetic Model – Uniform global geodetic model (topography, gravity, position) – Uniform global high resolution, high fidelity (color) mineralogical/compositional data – Uniform global high resolution morphology – Very high resolution (sub-meter) imaging outside of Apollo targets – Uniform global regolith characterization – Knowledge of interior of polar shadowed craters

Apollo Metric Camera Coverage

5 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) LRO Mission Overview Science and Exploration Objectives

Human adaptation Biological adaptation to lunar environment ) (radiation, gravitation, dust...)

Topography & EnvironmentsEnvironsEnvirons Understand the current state and evolution of the volatiles (ice)

Resources and other resources in context ( PolarGEOLOGYGEOLOGY Regions

ICE Develop an understanding of the PreparePrepare forfor HumanHuman Moon in support of human ExplorationExploration exploration (hazards, topography, navigation, environs) When • Where • Form • Amount

6 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) LRO Mission Overview (con’t) Suite of Six Science Instruments Instrument Benefit Deliverables

CRaTER Shielding Tissue equivalent (BU+MIT) constraints response to radiation Diviner Surface 300m scale maps of Temperature, surface (UCLA) temperatures ice, rocks LAMP Frosts? Maps of frosts in permanently (SWRI) “atmosphere”? shadowed areas, etc. LEND Ice in regolith Maps of water ice in (Russia) down to 1 m ? upper 1 m of Moon at 5km scales LOLA Precision, safe ~50 m scale polar navigation (3D) topography at < 1 m (GSFC) vertical, roughness LROC Landing 1000’s of 50cm/pixel images (125km2), and (NWU+MSSS) hazards and some entire Moon at 100m resources in UV, Visible

LRO Addresses National Academy Science Priorities for the Moon (NRC Decadal, 2002) 7 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) LRO Mission Overview (con’t) Flight Plan – Direct using 3-Stage ELV

• Launch on a Delta II class rocket into a direct insertion trajectory to the moon. • On-board propulsion system used to capture at the moon, insert into and maintain 50 km altitude circular polar reconnaissance orbit. • 1 year mission • Orbiter is a 3-axis stabilized, nadir pointed spacecraft designed to operate continuously during the primary mission. • LRO is designed to be capable of performing an extended mission of up to 4 additional years in a low maintenance orbit.

8 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) LRO Mission Timeline

• Feb. 2004 – Jun. 2004 PIP • Jun. 2004 – Oct. 2004 Program Review of AO Proposals • Oct. 2004 – Dec. 2004 AO Selection • Jan. 2005 – May 2005 Instrument Kickoff and Accommodations Review • May 2005 – Oct. 2005 PDR • Oct. 2005 – Jul. 2006 CDR • Jul. 2006 – Jul. 2007 Start of I&T • Jul. 2007 – Nov. 2007 PER • Nov. 2007 – Jul. 2008 Environmental Testing and PSR • Jul. 2008 – Sep. 2008 Launch site Preps and Launch • Sep. 2008 – Nov. 2008 LRO Commissioning and Start of Science • Nov. 2008 – Jan. 2010 50 ± 20 km Science Mission

9 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) Rapidly Evolving Spacecraft Concept

High Gain Antenna Instrument Deck

Ultra-Flex Solar Array

Major Design Issues: •Bi-prop versus mono-prop, & mono-prop with 1, 2, or 3 tanks, tanks inside or protruding? •Spacecraft packaging inside or “inside out” configuration? •All instruments on the optics deck or some located elsewhere? •Separate avionics and propulsion modules or integrated? 10 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) Current Spacecraft Concept

Solid Works Model TSS Geometry Model

LOLA

LAMP CRaTER LROC LEND

Diviner

X (Thrust)

PROP Y TANK RWAs Z (Nadir)

11 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) Lunar Thermal Environment

The lunar thermal environment is more severe than LEO, GEO, and Mars. It resembles the harsh Mercury environment.

LUNAR NIGHT LUNAR DAY 354 Hours without Sun 354 Hours with Sun Min. Surface Temp. is -280F (-173C, 100K) Max. Surface Temp. is 250F (121C, 395K)

Avg. Temp. of Lunar Surface over the course of 1 Earth Month

12 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) Lunar Thermal Environment (con’t)

Lunar Orbit Environment Parameters Hot Cold Nom Direct Solar [W/m2] 1420 1280 1368 Albedo 0.13 0.06 0.073

IR Max. [W/m2] 1320 1226 1268 (subsolar peak) IR Min. [W/m2] 5.2 5.2 5.2 (dark side)

Lunar IR Emission as a Function of Beta Angle

q”IR = [(C1-C2)*cos(β)*cos(θ)] + C2 where: q”IR = IR flux from Lunar surface C1 = peak flux at subsolar point C2 = minimum flux emitted from shaded Lunar surface β = Beta angle θ = Angle from subsolar point

13 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) LRO Thermal Design Challenges LRO Orbit Parameters: Type Lunar Circular Altitude 50±20km Inclination 90° (polar orbit) Orbit Period 113 minutes Full Sun Orbits Beta 90.0° to 76.4° (55 days/yr) Eclipsed Orbits Beta 76.4° to 0.0° (310 days/yr) Max. Eclipse 48 minutes (beta 0°) Beta 0o LRO Bounding Thermal Cases: Beta 0° is the Hot Op Case • Most severe IR loading • Zenith facing radiators flip through sun • Instrument apertures “see” sun near dawn and dusk 74°off bore site at 70 km Beta 90° is the Cold Op Case • Zenith facing radiators look at deep space • Minimal IR loading -Y Sun Pointing Safehold Attitude • Zenith facing radiators can be edge on to the moon Beta 90o 14 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) LRO Thermal Design Challenges (con’t)

• Class C mission Æ “single string” design for components – Cost, size, power, and mass constraints drive the thermal design to be a passive thermal design Æ challenge is that the lunar thermal environment is NOT benign • Radiator placement severely limited – Nadir pointing surfaces have too high of an IR loading to function as a radiator, especially at low Beta angles – Ram and wake surfaces also experience high IR loading at low Beta angles, combined with UV loading – Zenith surfaces are logical radiator locations, however, they also have a view of an atypically hot solar array • Solar array thermal design – Must take into consideration that the front side will have solar heating while at the same time the backside will receive lunar IR nearly equivalent to the solar flux in the worst hot operational case

15 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) LRO Thermal Design Challenges (con’t)

• Instrument optical bench is its own radiator – Instrument thermal control, in general, is achieved thru isolation from the lunar environment and by using passive means to conduct heat to a zenith radiator; note, however, some instruments require conductive isolation from optical bench, whereas some require conductive coupling to bench – Heaters on nadir facesheet at instrument interfaces are linearly coupled to a zenith facesheet which has a view to space Æ makes it difficult to minimize heater power in the worst case cold thermal conditions – Since optical bench size also has to be minimized due to mass constraints, it’s difficult to minimize thermal gradients and meet stability requirements • Thermal coatings requirements on instruments – Thermal design challenge for those instruments that require high emittance coatings (i.e., DIVINER) which also have direct and continuous views to the lunar surface – Several instruments with views to the sun have specularity requirements that limit the use of solar reflective coatings

16 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) LRO Thermal Design Challenges (con’t) Extreme temperature swing during operational cases as spacecraft travels from sun side to dark side of the moon O p t i c a l B e nc h R a di a t o r 40 LROC 30 C)

o 20 CRaTER 10

LOLA DIVINER 0 -1 0

LAMP Temperature ( -2 0 -3 0 12 34 56 Time (Hours) Temperature Gradients on the Optical Bench Nadir Facesheet 10 50 6.5 46 3.0 CRaTER 42 CRaTER 38 -0.5 LOLA -4.0 LEND 34 LOLA LEND -7.5 30 -11 26 -14.5 22 --18 Cold Case 18 Hot Case -21.5 14 -25 10 17 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) LRO Thermal Design Challenges (con’t)

• Critical understanding of heater power profile as a function of beta angle for power margin verification is required early on

Heater Power vs. Beta Angle for LEO and LRO Missions

SA Capability

) LRO W ( r e w Po

LEO, typ.

020406080100 Beta Angle (Deg)

18 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) Lessons Learned from Early Modeling • Identified sensitivities – Thermal performance of instruments is very sensitive to the linear coupling from the instrument optical bench to the spacecraft – Thermal masses of instruments must also be modeled correctly

• Discovered potential “cross talk” between optical bench heaters that are in proximity to one another

• Instrument designs are highly dependent upon understanding the heat flow across the interface between the optical bench and each instrument

• Thermal control on the instrument optical bench is most effective when the instruments are conductively isolated from the bench, but since LRO forced to take a different approach, modeling required to optimize location of instruments on bench

• In order to minimize heater power for battery (has strictest temperature limits of all avionics), it should be placed on the zenith radiator which has a direct view to solar array in Beta 90 case

19 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) Beyond LRO?

Beyond LRO? Exploration of a potential resource: Validation of water ice Some options… and in situ biological sentinel experiments?

Beyond LRO?: Follow-on to LRO, filling key gaps, including regolith characterization in 3D, far-side gravity, landing site hazards, Beyond LRO? Potential lunar Telecomm. experiment returns and demos? infrastructure? 20 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO) Conclusions

• LRO seeks to answer many pressing questions about the moon in preparation for future manned missions • LRO has an aggressive schedule in order to meet the 2008 launch date • The Lunar thermal environment is as severe as Mercury and it poses many design challenges that typical LEO and interplanetary missions don’t need to address • Numerous instruments with different requirements for coupling to an optical bench that functions as its own radiator poses a difficult thermal problem that requires careful analysis • Early thermal analysis has been extensive and strives to keep pace with a rapidly evolving mechanical design • Stay tuned for PDR analysis and design effort!

21 NASA’s Goddard Space Flight Center Lunar Reconaissance Orbiter (LRO)